This invention relates to ship propulsion systems, and more particularly to an improved propulsion system control which provides a more rapid response when the ship is maneuvering at low vessel speeds.
A common form of marine propulsion system uses ahead and astern air actuated clutches for connecting the prime mover to a reversing reduction gear unit which drives the propeller. The air actuated clutches are engaged by inflation and the degree of clutch engagement can be controlled by controlling the amount of inflation. A pneumatic control system is typically provided for selecting the ahead or astern clutches, for controlling the clutch inflation, and for controlling an engine speed governor which determines the engine speed. A single throttle lever apparatus can be provided for controlling both the clutch engagement and engine speed by movement of the lever from neutral towards either an ahead or astern direction. Examples of such a control for a ship's propulsion system is found in U.S. Pat. No. 3,727,737 of John M. Phinney, issued Apr. 17, 1973 for "Pressure Modulating System for reversing Clutches and Throttle Control" and U.S. Pat. No. 4,072,221 issued Feb. 7, 1978 for "Marine Clutch and Throttle Governor Control System."
In the systems of these earlier patents, a pneumatic clutch control assembly for a ship's propulsion system is sequentially operated to regulate the inflation of ahead and astern air infatable clutches and to also control the prime mover speed. The control assembly is actuated by a single throttle lever located on a pilot house control stand. Movement of the lever in one direction provides forward rotation of a propeller at a speed which increases with handle travel away from neutral. Movement of the handle in the opposite direction provides astern rotation of the propeller with speed increasing as the handle is moved farther from neutral. The center position provided a neutral setting in which the engine is disconnected from the propeller and no power is transmitted, although the engine continues to idle.
The single lever control of both direction and speed is accomplished in the following manner: As the lever is pivoted in either direction from neutral, air is supplied to a selector valve which selects one or the other of the ahead or astern clutches. Thereafter, and up to a first control pressure, air pressure proportional to the position of the lever away from neutral is fed through a first valve to the selected clutch and begins inflating the selected clutch. During this time the engine remains at idle speed. After a first control pressure is reached, the first valve is piloted and a second path for air to the clutch is established. This second path has provision for an initial programmed rate of feed of air to the clutch through a choke valve so as to softly inflate the clutch. Upon reaching a second higher control pressure, full supply air pressure is connected to the clutch. After the first control pressure is reached, the continued inflation of the clutch is not dependent upon the position of the throttle lever.
When the air pressure within the clutch rises to a predetermined level, the control of these earlier patents pilot a governor valve which, in effect, connects the throttle lever control to the speed governor of the engine so that the pressure supplied to the governor directly corresponds to the position of the throttle lever and the engine speed is controlled by movement of the throttle lever. The throttle lever setting determines only the final operating speed and direction and all intermediate steps of clutch engagement and inflation, and engine governor speed are handled automatically by the control system.
Since the control systems of the prior art carry out their clutch and engine speed control in a sequential manner and the clutches are inflated to full inflation in a controlled manner through the programmed choke valve, there is a noticeable delay in response when the throttle lever is moved from neutral to a position for low speed. Such a condition is encountered during typical maneuvering. I have developed an improved control system which accomplishes rapid clutch engagement at low speeds to thereby provide a more rapid response during normal maneuvering of the vessel.